Well Sakurai was dumb enough to remove Mewtwo so...*shrug*
To be fair, Mewtwo was planned to show up, but was removed due to time constraints. If Ike gets cut, it'd be for the same reason.
I have to admit that I'm a little worried for Mewtwo's chances. Sure he's immensely popular, but that popularity didn't help poor Ridley too much.
I understand the concern, but Mewtwo isn't in a similar situation to Ridley here.
Ridley faced several problems that will likely contribute to his non-inclusion to this game. First is that what he is massively popular in the West; he barely gets any request whatsoever in Japan. ChronoBound, the most prominent Ridley supporter out there you can find, has mentioned that barely anyone mentioned Ridley every time he went to Japanese message boards. Ridley also has the issues of Sakurai not only
dismissing him as a playable character shortly after Brawl, but considering him too difficult to work with as well as hints towards being in a non-playable role in this game.
Mewtwo on the other hand is the most wanted character worldwide; surpassing even Mega Man in want (who was the most wanted newcomer) and making him essentially SSB4's Sonic. Sakurai added Mewtwo into Melee and planned for Mewtwo to be in every single Smash game to date; so Sakurai obviously sees Mewtwo as playable material. As for this game, Sakurai has been hinting that Mewtwo will return again and with everything Mewtwo has going for it (e.g. everything), not only am I confident in Mewtwo's return, I expect Mewtwo to be prioritize above at least Lucario and Jigglypuff (keep in mind that Sakurai did state that Lucario probably would have been cut if they didn't expand the roster, just look at the POTD for Lucario's confirmation).
The difference is that Sakurai has said before that Ridley would be difficult to make. Sure, he said they MAY have been able to do it, but they would have to put their best efforts into it, and he probably didn't think it was worth the time and effort to make him playable.
This is the same man that made third-parties possible despite declaring them in some ways, harder than making the game and likely bringing even more third-parties in to this game (Mega Man, Sonic and Pac-Man if the leak is true). Oh and Sakurai is no stranger to adding characters that are very difficult to work with (Ice Climbers in Melee, Olimar in Brawl, Rosalina & Luma). To say that Ridley isn't worth the effort to add reeks of hypocrisy on Sakurai's behalf. Supporters have every right to criticize Ridley's exclusion for that reason alone.